It is known to produce stitches which are generally described as interlooped stitches, from a single thread by forming a loop and drawing this loop around adjacent portions to other stitches, in effect to form a chain or chain-like structure.
The variety of such stitches is manifold and the present invention is particularly concerned with one class of such stitches in which the thread is alternately visible and invisible on one side of the fabric and appears to be visible continuously along the seam on the opposite side of the fabric, i.e. the one side of the fabric shows the thread in spaced apart stitches which do not appear to be interconnected at this side of the fabric. It is such a stitch type having thread loops reaching over to this side of the fabric and wherein the thread is alternately visible and invisible i.e. wherein the loops appear to be spaced apart without any connection, that is the concern of this invention.
Two such stitch types, by way of example, are stitch type 104 (chain stitch) of the Federal Standard No. 751a and stitch type 209 (saddler and row stitch). Similar stitches are recognized in the German Industrial Standard DIN 61 400.
In the formation of such stitches, on one side of the fabric there appears to be a free space between the successive stitches, a construction which has ornamental advantages and which gives the appearance of hand stitching. Such stitch types are widely used in the garment industry, especially when particularly esthetic or ornamental results are desired with a stitch seam which nevertheless is effective for the fixing of parts of the garment together or for other structural purposes.
The chain stitch 104 is sewn with the aid of two mutually parallel juxtaposed needles, a factor which makes the passage of the seam around corners or with angular portions difficult to achieve neatly.
Furthermore, the spacing between the holes in the fabric spanned by each visible stitch is fixed by the distance between the needles and thus either cannot be altered or can be altered only with considerable difficulty. In addition, the individual stitches formed by the loop which passes through one hole or piercing and a successive hole or piercing, is not locked within one of these holes or otherwise firmly anchored, but rather each loop is merely chained to the next loop on the underside of the fabric so that upon breakage or release of an end of the seam, raveling or loosening of the entire stitch seam may occur. In many ways, therefore, this stitch seam cannot be utilized for structural purposes, i.e. for holding two parts tightly together, but must be treated as a purely decorative stitch seam.
Stitch type 209 has other disadvantages. Firstly, it must be formed with a yarn of limited length, generally 1.5 m, which limits the length of the seam which can be sewn. When the thread is expended, the sewing machine must be stopped and a new thread introduced in a highly time-consuming and inconvenient operation.
In German Pat. DE No. 26 38 264, there is described an apparatus for forming stitch seams with the stitch type 209, but in the formation of such stitches there is always the danger that the fabric will be crimped or bunch up when tension is applied to the thread. This again is because the individual stitches are not truly locked together or secured.
There are, of course, other stitch types in which the stitches are firmly locked against these disadvantageous phenomena, but such stitches do not have the esthetic appearance of stitch types 104 and 209.